Velocity-reduced drive system

ABSTRACT

A velocity-reduced drive system (1) is used to operate a movable member of a video camera or a combined camera-and-VTR unit at a reduced velocity. The drive system comprises a micro or flat motor (5) supported in cases (2), (3) and (4), a worm gear (6) rotatably supported by the cases, a worm wheel meshed with the worm gear, first power transmission means (11), (12) and (12) for transmitting rotational force of the motor (5) to the worm gear (6), and second power transmission means (14), (15) and (16) for transmitting rotational force of the worm gear (6) to an output shaft (7) to be coupled to the movable member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a velocity-reduced drive system, and moreparticularly to a small or flat velocity-reduced drive system foroperating a small device like a video camera or a combinedcamera-and-video-tape-recorder unit by reducing the velocity of a motor.

2. Description of the Related Art

It is necessary to reduce the velocity of a motor for a lens drivingunit when such unit is operated for focusing or zooming a video cameraor a combined camera-and-video-tape-recorder unit (hereinafter calledcamera-and-VTR unit). One of such velocity-reduced drive systems wasproposed in Japanese Patent Laid-Open Publication No. 74342/1989. Withthe cited system, the velocity of the motor is reduced by a reductiongear train or by combination of the reduction gear train and apulley-belt unit. A drive shaft of the motor and an output shaft arepositioned in the same direction.

Conventionally, the motor and a case for the reduction gear unit arepiled with the drive shaft and the output shaft facing in the samedirection. Therefore, the drive shaft inevitably becomes longer. Thereduction gear train includes a plurality of spur gears, which generaterelatively high sounds. Such high sounds are picked up by a microphoneof the video camera, being reproduced as noises. Since the direction ofthe output shaft is limited, the velocity-reduced drive system wouldhave narrower application fields. Further, a number of the spur gearshave to be used to obtain large velocity reductions, which meansincrease of component parts.

When the velocity-reduced drive system is used to operate a cylindricalmovable member (e.g. a lens barrel of a combined camera-and-VTR unit),there would be formed an undesired space around the flat surface of thedrive system and the cylindrical member.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide avelocity-reduced drive system which is compact, being able to obtainlarge velocity reductions, and to suppress noises.

A further object of the invention is to provide a velocity-reduced drivesystem which is suitable for operating a movable member of a videocamera or a combined camera-and-VTR unit.

A still further object of the invention is to provide a velocity-reduceddrive system which is suitable to operate a cylindrical movable member,being compact to save a useless space between the drive system and thecylindrical movable member.

According to the invention, there is provided a velocity-reduced drivesystem comprising: a micro or flat motor for producing a relativelylarge torque and mounted in a case, and a reduction gear unit. Thereduction gear unit includes a worm gear, a first power transmissionmeans for transmitting rotational force of the motor to the worm gear, aworm wheel meshed with the worm gear, and a second power transmissionmeans for transmitting rotational force of the worm gear to an outputshaft.

The output shaft has a coupling member via which it is coupled to amovable member to be operated at a reduced velocity.

When the drive system is applied to a movable member such a lens barrelof a video camera, the drive shaft of the motor is positioned inparallel with the worm gear. With respect to a plane formed by the firstpower transmission means, the motor is remote from the movable member,and a reduction gear unit is near the movable member. Further, the motorand the reduction gear unit are arranged along an imaginarycircumference whose center agrees with the movable member.

Rotational force of the motor is reduced its velocity while it is beingtransmitted to a destination, i.e. the movable member, via the firstpower transmission means, worm gear, worm wheel, second powertransmission means, and output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a velocity-reduced drive systemaccording to a first embodiment of the invention, taken along line 1--1of FIG. 2;

FIG. 2 is a front view of the velocity-reduced drive system of FIG. 1;

FIG. 3 is a front view of a gear train between a worm and an outputshaft;

FIG. 4 is a side elevational view of a power transmission system betweena motor drive shaft and the output shaft;

FIG. 5 is a side cross-sectional view of cases for supporting a wormgear, a worm wheel and output shaft;

FIG. 6 is a front view of the cases and output shaft, in exploded form;

FIG. 7(a) is a front view of a first case;

FIG. 7(b) is a cross-sectional view taken along line 7b--7b of FIG.7(a);

FIG. 7(c) is a cross-sectional view taken along line 7c--7c of FIG.7(b);

FIG. 8 is a rear view of a velocity-reduced drive system according to asecond embodiment of the invention, with a second case removed;

FIG. 9 is a cross-sectional view taken along line 9--9 of FIG. 8;

FIG. 10 is a cross-sectional view taken along line 10--10 of FIG. 8;

FIG. 11(a) is a rear view of a first case;

FIG. 11(b) is a cross-sectional view taken along line 11b--11b of FIG.11(a);

FIG. 11(c) is a front view of the first case;

FIG. 12(a) is a front view of the second case;

FIG. 12(b) is a cross-sectional view taken along line 12b--12b of FIG.12(a);

FIG. 12(c) is a cross-sectional view taken along line 12c--12c of FIG12(a);

FIG. 12(d) is a cross-sectional view taken along line 12d--12d of FIG.12(a);

FIG. 12(e) is a left-side elevational view of the second case;

FIG. 12(f) is a rear view of the second case;

FIG. 13(a) is a plan view showing the internal configuration of avelocity-reduced drive system according to a third embodiment;

FIG. 13(b) is a front sectional view of the velocity-reduced drivesystem of FIG. 13(a);

FIG. 14 is a side elevational view of the velocity-reduced drive systemof FIG. 13(a);

FIG. 15 is a cross-sectional view showing part of an input gear fittedover the drive shaft;

FIG. 16(a) is a plan view of a first case;

FIG. 16(b) is a cross-sectional view taken along line 16b--16b of FIG.16(a);

FIG. 16(c) is a cross-sectional view taken along line 16c--16c of FIG.16(a);

FIG. 17(a) is a bottom view of a second case;

FIG. 17(b) is a cross-sectional view taken along line 17b--17b of FIG.17(a);

FIG. 17(c) is a front sectional view of the second case;

FIG. 17(d) is a plan view of the second case;

FIG. 17(e) is a cross-sectional view taken along line 17e--17e of FIG.17(a);

FIG. 18 is a front sectional view of a velocity-reduced drive systemaccording to a fourth embodiment;

FIG. 19 is a side elevational view of the velocity-reduced drive systemof FIG. 18;

FIG. 20 is a top sectional view of units around a drive shaft of thesystem of FIG. 18;

FIG. 21 is a perspective view showing the relationship between a flatmotor, reduction gear unit and output shaft; and

FIG. 22 is a front view showing main parts of a modified example of thefourth embodiment.

DETAILED DESCRIPTION

FIGS. 1 to 7 show a velocity-reduced drive system according to a firstembodiment of the invention. The velocity-reduced drive system 1(hereinafter called "drive system 1") comprises first to third cases 2,3, 4, a flat motor 5, a worm gear 6, an output shaft 7, a first powertransmission means, and a reduction gear train 8 as a second powertransmission means. The motor 5 is housed in the first case 2 (FIG. 7).The worm gear 6 is rotatably supported by the first and second cases 2,3. The output shaft 7 is rotatably supported by the first and thirdcases 2, 4. The first power transmission means transmits rotationalforce of the motor to the worm gear 6. The reduction gear train 8rotatably couples the output shaft 7 and worm gear 6.

The motor 5 includes a drive shaft 5b received in a bearing 5aa fixed toa motor case 5a. The motor case 5a is made of magnetic material, havinga fold 5c (only one is shown in FIG. 1), which is inserted through abase plate 10 of magnetic material, being bent to be fixed on the baseplate 10.

A circular coil and a commutator which are hardened by synthetic resinare attached to the drive shaft 5b. A magnet and a brush are fixed onthe base plate 10. A terminal integral with a brush holder (not shown)projects through a hole 10a of the base plate 10. Part of the base plate10 is used as a motor case. The motor 5 is mounted on a motor space 2ain the first case 2.

The base plate 10 is fastened to the first case 2 by screws (not shown)in screw holes 9 (shown in FIGS. 6 and 7). The base plate 10 has acoupling member 10b which is used to couple the drive system 1 to a bodyof a video camera, for example.

The drive shaft 5b projects from the motor 5 through a window 2b of thefirst case 2. A small drive pulley 11 is tightly fitted over theprojecting end of the drive shaft 5b.

The worm gear 6 is in parallel with the drive shaft 5b, having one end6a received in a bearing hole 2d and the other end 6b received in abearing groove 2e of the first case 2. The ends 6a, 6b are covered by aflat bearing cover 3a (shown in FIGS. 5, 6) of the second case 3, sothat the worm gear 6 is rotatably supported by the first and secondcases 2, 3. The opposite ends of the worm gear 6 are conical to decreasea frictional resistance in the bearing hole 2b or the bearing groove 2eduring the forward or backward rotation.

One end of the worm gear 6 projects from the first case 2, carrying alarge driven pulley 12 tightly fitted thereon. The driven pulley 12serves to reduce the velocity of the motor 5. An endless belt 13 iswound around the driven pulley 12 and the drive pulley 11. The pulleys11, 12 and the endless belt 13 constitute the first power transmissionmeans for transmitting the rotational force of the motor 5 to the wormgear 6.

A worm wheel 14 is meshed with the worm gear 6, being is rotatablysupported over a small diameter portion 7a of the output shaft 7. Theoutput shaft 7 is rotatably supported in a bearing hole 2f of the firstcase 2 and a bearing hole 4a of the third case 4. The worm wheel 14 hasa small spur gear 14a as an integral part.

The reduction gear train 8 functions as the second power transmissionmeans to transmit the rotational force of the worm gear 6 to the outputshaft 7, including the worm wheel 14, reduction gear 15, and a spur gear16 as shown in FIG. 3. The spur gear 16 is tightly fitted over theportion 7b of the output shaft 7. The reduction gear 15 is meshed withthe small spur gear 14a of the worm wheel 14.

Axial movement of the worm wheel 14 is controlled by an end surface 2faof a sleeve forming the bearing hole 2f of the first case 2 and by astep 7ba of the portion 7b of the output shaft 7b.

The reduction gear 15 is rotatably supported around a shaft 17, which isrotatably supported with its opposite ends respectively received in ahole 3b of the second case 3, and a hole 4b of the third case 4 (FIG.6). As shown in FIG. 3, the reduction gear 15 is a double gear, having alarge spur gear 15a and a small spur gear 15b. The large spur gear 15ais meshed with the small spur gear 14a, while the small spur gear 15b ismeshed with the spur gear 16.

The cases 2, 3, 4 for supporting the worm gear 6, worm wheel 14 andreduction gear train 8 are fastened one another as shown in FIG. 6.Specifically, the third case 4 is fastened to the second case 3 byengaging pins 4c, 4d of the third case 4 with through holes 3c, 3d ofthe second case 3. Then, the second and third cases 3, 4 are fastened tothe first case 2 by engaging a pin 2g of the first case 2 with thethrough hole 3c of the second case 3. Thereafter, the screws inserted inthe through holes (not shown) of the second and third cases 3, 4 areforcibly thrust into screw holes 2h, 2i (FIG. 7) of the first case 2.

As shown in FIGS. 1, 2 and 4, a pulley cover 18 is attached to the firstcase 2 by screws 19, 20 so that the pulley cover 18 confronts with theend 6c of the worm gear 6 and covers the driven pulley 12. Specifically,the pulley cover 18 is located very near the end 6c of the worm gear 6to minimize the axial movement of the worm gear 6 when it is rotated.The first case 2 has a cut 2k through which a lubrication agent issupplied to the worm gear 6 as shown in FIG. 7.

The drive system 1 will be assembled in the following order. Firstly,the base plate 10 of the motor 5 attached with the drive pulley 11 isfastened to the first case 2 by screws. The worm gear 6 having thedriven pulley 12 thereon is placed in a bearing hole 2d and a bearinggroove 2e of the first case 2. The second and third cases 3, 4 carryingthe output shaft 7 and the reduction gear train 8 in combination arepositioned on the first case 2, being fastened by screws. Under thiscondition, one end of the output shaft 7 is placed in a bearing hole 2fof the first case 2, and the worm wheel 14 is meshed with the worm gear6. The endless belt 13 is trained around the drive and driven pulleys11, 12. Since the drive shaft 5b of the motor 5 and the worm gear 6 arein parallel, the endless belt 13 can be easily trained around thepulleys 11, 12. Finally, the pulley cover 18 is attached to the firstcase 2 by screws.

The following are example of dimension of some main components. The wormgear 6 is approximately 2 mm in the diameter. The worm wheel 14 to bemated with the worm gear 6 is approximately 4.8 mm in the diameter. Thecase 2 is approximately 23.7 mm long, and approximately 5.9 mm thickincluding the base plate 10. The motor space in the case 2 is 15 mm×15mm.

Operation of the drive system 1 will be described hereinafter. When themotor 5 rotates in one direction (e.g. forwardly), the rotational forceof the drive shaft 5b is transmitted via the drive pulley 11, endlessbelt 13, and driven pulley 12 to the worm gear 6, where the velocity ofthe rotational force has been remarkably reduced. When the worm gear 6meshed with the worm wheel 14 is rotated, the end 6a of the worm gear 6is in contact with the bottom of the hole 2d of the first case 2.Rotational force of the worm wheel 14 meshed with the worm gear 6 isfurther reduced in velocity, being transmitted via the reduction geartrain 3 (FIG. 3) to rotate the output shaft 7.

When the motor 5 rotates in the opposite direction (i.e. backwardly),the worm gear 6 meshed with the worm wheel 14 is rotated with itsconical end 6c in contact with an inner surface 18a of the pulley cover18, reducing the rotating velocity of the worm wheel 14.

The motor 5 and the velocity reduction unit are juxtaposed so that thediameter of the driven pulley 12 coupled with worm gear 6 can be madelarge enough to obtain large velocity reductions between the motor andthe worm gear. This means that the reduction gear train 8 is notrequired to reduce the velocity so extensively, thereby suppressingnoises caused by the reduction gear train.

In the foregoing embodiment, the portion 7a of the output shaft 7 isused to rotatably support the worm wheel 14, which decreases the numberof component parts.

The flat motor is effective to reduce the size of the whole drivesystem. The pulley, endless belt, worm gear and worm wheel incombination are also effective to attain large velocity reductions andsubstantially quiet operation. Combination of the worm gear and the wormwheel enables the output shaft to be positioned as desired, so that thewhole drive system can be designed according to a space where the drivesystem is used.

With the foregoing embodiment, the first case 2 and the motor case 2aare separate members. However, it is also possible to make them as oneunit by pressing a sheet metal to form the first case 2 and to stamp themotor space (2a) thereon, thereby decreasing the number of the componentparts and facilitating the assembling work.

A velocity-reduced drive system according to a second embodiment will bedescribed with reference to FIGS. 8 to 12. This embodiment ischaracterized in that a worm gear and a worm wheel are used in place ofthe spur gears in the reduction gear train 8 of the first embodiment.

The thin drive system 21 comprises coupled first and second cases 22,24, a flat motor 25, a first worm gear 26, a first power transmissionmeans, a second power transmission means 31, and an output shaft 27. Theflat motor 25 put in a motor case 25a is housed in the first case 22(FIG. 11). The first worm gear 26 and the output shaft 27 arerespectively and rotatably supported by the first and second cases 22,24. The first power transmission means transmits the rotational force ofthe motor 25 to the first worm gear 26. The second power transmissionmeans 31 includes the first worm gear 26, output shaft 27, worse wheel28, second worm gear 29 and second worm wheel 30. The first worse wheel28 rotatably couples the output shaft 27 and the first worm gear 26.

The motor 25 has a drive shaft 25b projecting from the motor case 25a.The motor case 25a is attached on a motor space 22a of the first case 22with members 25c fastened by a pair of screws 32. The first case 22 hasa coupling member 22b for attaching the drive system to a combinedcamera-and-VTR unit, for example.

One end of the drive shaft 25b projects through a window 22c of thefirst case 22, having a small drive pulley 33 tightly fittedtherearound.

Opposite ends 26a, 26b of the first worm gear 26, which is in parallelto the drive shaft 25b, are respectively received in bearing holes 22d,24a of the first and second cases 22, 24, so that the worm gear 26 isrotatably supported by the cases 22, 24. The end 26b of the first wormgear 26 is conical to reduce the frictional resistance during therotation of the worm gear 26.

A large driven pulley 34 for velocity reduction is tightly fitted overan end 26c of the worm gear 26 extending through the bearing hole 22d.An endless belt 35 is trained around the drive and driven pulleys 33,34. The drive and driven pulleys 33, 34 and the endless belt 35constitute the first power transmission means for transmitting therotational force of the motor 25 to the first worm gear 26.

The first case 22 has a protector 22s for protecting the pulleys 33, 34and the endless belt 35.

The first worm wheel 28 meshes with the first worm gear 26. The wormwheel 28 is tightly fitted over one end 29a of a second worm gear 29.The second worm gear 29 is rotatably supported by the first case 22 withopposite ends 29a, 29b received in bearing holes 22e, 22f and covered bybearing covers 24b, 24c of the second case 24. The ends 29a, 29b of thesecond worm gear 29 are conical to decrease the frictional resistanceduring the rotation of the worm gear 29.

Tightly fitted over a knurled portion of the output shaft 27, the secondworm wheel 30 is meshed with the second worm gear 29. The first wormwheel 28, second worm gear 29 and second worm wheel 30 constitute thesecond power transmission means for transmitting the rotational force ofthe first worm gear 26 to the output shaft 27.

The output shaft 27 is rotatably supported by the first and second cases22, 24 with the small diameter portions 27a, 27b thereof received inbearing grooves 22h, 22i of the first case 22 and covered by bearingcovers 24d, 24e of the second case 24.

A spacer 36 is fitted over the output shaft 27 at its portion betweenthe second worm wheel 30 and the bearing hole 22i of the first case 22.The output shaft 27 is attached over its end (not shown) a pinion gearfor operating a focusing ring, for example.

The second case 24 is fastened to the first case 22 by fittingprojections 24h, 24i thereof into holes 22k, 22m of the first case 22,and fitting screws 37, 38, (which are inserted in through holes 24k,24m), into holes 22n, 22p of the first case 22.

In operation, when the motor 25 is rotated in one direction, therotational force of the motor 25 is transmitted via the drive pulley 33,belt 35 and driven pulley 34 to the first worm gear 26, which receivesthe rotational force having a reduced velocity. The first worm gear 26sends its mating first worm gear 28 its rotational force having alargely reduced velocity, thereby rotating the first worm gear 29integral with the worm wheel 28. The second worm gear 29 rotates itsmating second worm wheel 30 at a very reduced velocity, which rotatesthe output shaft 27 integral therewith.

The drive system of this embodiment is as advantageous as the drivesystem of the foregoing embodiment. In addition, this drive system canenlarge a range to install the output shaft, obtain large velocityreductions, and suppress noises caused by the reduction gear train.

FIGS. 13 to 17 show a velocity-reduced drive system of a thirdembodiment of the invention. As shown in FIG. 13 and 14, the drivesystem 101 comprises a micro motor 102 (only partially shown), first andsecond cases 103, 104, a first worm shaft 105, a second worm shaft 106,and an output shaft 107. The first and second worm shafts 105, 106 arerotatably supported by the first and second cases 103, 104.

The motor 102 is fastened to the first case 103 by screws 109 which areinserted through a case cover 108 and through the second and first cases104, 103.

The motor 102 has axially a long oval shape, including a drive shaft102a projecting into the first case 103. An input gear 102b made ofsynthetic resin is tightly fitted over the drive shaft 102a (to bedescribed later).

The first worm 105 shaft has, as integral parts, a spur gear 105a to bemeshed with the input gear 102b, and a first worm gear 105b. The firstworm shaft 105 is rotatably supported by the first and second cases 103,104 with opposite ends 105c, 105d thereof respectively received in abearing hole 103a of the first case 103 (FIG. 16) and a bearing hole104a of the second case 104 (FIG. 17). The input gear 102b and the spurgear 105a constitute a first power transmission means for transmittingthe rotational force of the motor 102 to the first worm gear 105b.

The configuration of the input gear 102b will be described referring toFIG. 15. The input gear 102b is made of synthetic resin, having atoothed portion 102ba to be meshed with the spur gear 105a, and a hub102bb. The length L2 of the hub 102bb, i.e. the whole length of theinput gear 102b, is larger than the width L1 of the toothed portion102ba. For example, the input gear 102b has the following dimension:approximately 3.2 mm in the diameter, approximately 1.4 mm in the widthL, approximately 3.2 mm in the whole length L2, and approximately 2 mmin the hub diameter. The input gear 102b is tightly fitted over thedrive shaft 102a (approximately 1 mm in the diameter) via the centerhole 102bc thereof. The input gear 102b is lengthened so that it is moretightly fitted over the drive shaft 102a of the motor 102 and is notthrust in its rotating direction and axially on the drive shaft 102a. Inthis embodiment, although the width L1 of the toothed portion is smallerthan the length L2 of the hub, it is also possible to make L1 equal toL2 when there is a sufficient space for the input gear 102b.

The second worm shaft 106 has a first worm wheel 106a to be meshed withthe first worm gear 105b, and a second worm gear 106b as integral parts.Opposite ends 106c, 106d of the second worm shaft 106 are respectivelyreceived in bearing grooves 103b, 103c of the first case 103. These ends106c, 106d are covered by bearing covers 104b, 104c of the second case104 (FIG. 17) so that the second worm 106 is rotatably supported by thefirst and second cases 102, 104.

As shown in FIG. 14, the output shaft 107 is rotatably supported by thefirst case 103 with opposite ends 107a, 107b thereof respectivelyreceived in a bearing hole 103d of the first case 103 and a bearing hole108a of the case cover 108. A second worth wheel 107c, to be meshed withthe second worm gear 106b, is tightly fitted over the output shaft 107between the first case 103 and the case cover 108, i.e. in a space 104dof the second case 104 (FIG. 17(a)).

The first worm wheel 106a, second worm gear 106b and second worm wheel107c constitute a second power transmission means for transmitting therotational force of the first worm gear 105b to the output shaft 107.

A hub on one side of the worm wheel 107c has a key way 107d. The hub istightly fitted into an output gear 107e. As shown in FIG. 13 and 14,part of the output gear 107e is projected from the cases 103, 104 to becoupled to a tape loading unit (not shown). In this embodiment, theoutput gear 107e is rotated with the output shaft 107. However, it isalso possible to extend one end 107b of the output shaft 107 to receivea pinion as an output gear, which will be rotatably coupled to thedevice to be operated by the drive system.

The first and second cases 103, 104 are fastened by inserting pins 103e,103f of the first case 103 (FIG. 16) in positioning holes 104e, 104f ofthe second case 104 (FIG. 17). The case cover 108 is attached to thesecond case 104 by fitting a projection 104h (FIG. 17) of the case 104in a positioning hole 108b (FIGS. 13 and 14) of the case cover 108, andby inserting a pin 104k into a positioning hole (not shown) of the case104. The case cover 108 has a pair of coupling holes 108c for couplingthe drive system 101 to an immovable member such as a body of the videocamera, as shown in FIG. 13. In FIG. 16, reference numerals 103m, 104mdenote a pair each of through holes into which a pair of fasteningscrews 109 are (FIG. 13) are inserted.

In operation, when the drive shaft 102a of the motor 102 rotates in thedirection shown by the arrow in FIG. 13, the input gear 102b, which isintegral with the drive shaft 102a, rotates the first worm 105 as wellas the spur gear 105a in the direction shown by the arrow. Therotational force of the first worm shaft 105 is transmitted via thefirst worm gear 105b and the first worm wheel 106a to the second wormshaft 106, which is then rotated at a reduced velocity in the directionshown by the arrow.

The rotational force of the second worm 106 is transmitted via itssecond worm gear 106b to the second worm wheel 107c, which receives therotational force having a reduced velocity, rotating the output shaft107 integral with the worm wheel 107c at a further reduced velocity inthe direction shown by the arrow. The rotational force of the outputshaft 107 is transmitted via the output gear 107e to the destination,not shown. When the motor 102 rotates in the opposite direction, all therelated members of the drive system are rotated in the oppositedirections.

In the foregoing embodiment, the motor and the first worm shaft arerotatably coupled by the spur gears, so that no thrust will be exertedto axially move the drive shaft of the motor. Therefore, the motor canreliably rotate in the forward or backward direction. Since no thrustpreventing measures are necessary, the drive system can be simplified.Two sets of the worm gear and worm wheel combination are employed toobtain large velocity reductions, decreasing the number of componentparts. The hub of the input gear 102b of the synthetic resin is longenough to be reliably and tightly fitted over the drive shaft 102a ofthe motor 102, thereby decreasing noises and manufacturing cost of thedrive system. These features are very advantageous when the drive systemis applied to a small device such as a combined camera-and-VTR unit.

A velocity-reduced drive system of a fourth embodiment will be describedhereinafter with reference to FIGS. 18 to 22. The drive system isintended for use with a cylindrical movable member such as a lens barrelof a combined camera-and-VTR unit.

As shown in FIG. 18, the drive system 211 is positioned near the lensbarrel 210 of the combined camera-and-VTR unit. The drive system 211comprises a flat motor 212 as a drive source, a reduction gear unit 213,a first power transmission means 214, and an output shaft 215. The firstpower transmission means 214 transmits the rotational force of the motor212 to the reduction gear unit 213. The output shaft 215 transmits therotational force of the reduction gear unit 213 to the lens barrel 210.The reduction gear unit 213 reduces the velocity of the motor 212. Inthis embodiment, the reduction gear unit 214 includes a first worm gear213a for receiving the rotational force of the motor 212, and a secondpower transmission means for transmitting the rotational force of theworm gear 213a to the output shaft 215. The velocity reduction unit 214will be described in detail later.

The motor 212 is placed on one side of a base plate 216 which is locatedalong a tangent of the lens barrel 210, i.e. on the side opposite to theside confronting the lens barrel 210. A drive shaft 212a of the motor212 carries a small drive pulley 214a. The base plate 216 serves as partof a case.

The reduction gear unit 213 is rotatably supported by the base plate 212and a unit case 217 on the base plate 216, being located on the baseplate 216 on the side opposite to the motor 212, i.e. on the sideconfronting the lens barrel 210. The reduction gear unit 213 includestwo sets of the worm gear and worm wheel combination.

The reduction gear unit 213 includes a first worm gear 213a formed onthe first worm shaft. The first worm shaft is parallel to the driveshaft 212a. The first worm shaft is rotatably supported with its one end213aa projecting through a bearing hole 216a of the base plate 216, andthe other end 213ab thereof received in a bearing hole 217b of the unitcase 217. The first worm wheel 213b has a second worm gear 213c as anintegral part. The worm gear 213c is meshed with which a second wormwheel 213d. The first worm wheel 213b, second worth gear 213c, andsecond worth wheel 213d constitute the second power transmission means.

The first worm wheel 213b and the second worm gear 213c are axiallyintegral with each other on the second worm shaft. The second worm shaftis rotatably supported by the base plate 216 and the unit case 217 withends 213ba, 213ca of the second worm shaft respectively received inbearing grooves 216b, 216c of the base plate 216 and covered by bearingcovers 217a, 217b of the unit case 217.

The output shaft 215 is rotatably supported by the unit case 217 and thebase plate with a small diameter portion 215a received in bearinggrooves 217c, 217d of the unit case 217 and held by bearing covers 216d,216e of the base plate 216. The second worm wheel 213d, which is meshedwith the second worm gear 213c, is tightly fitted over the knurled areaof the small diameter portion 215a of the output shaft 215. The end 215bof the output shaft 215 extends toward a toothed portion (not shown) ofthe lens barrel 210, having a pinion 215c tightly fitted thereon to meshwith the toothed portion.

The first power transmission means 214 includes a small drive pulley214a, a large driven pulley 214b, and an endless belt 214c. The smalldrive pulley 214a is tightly fitted over the drive shaft 212a of themotor 212. The large driven pulley 214b is tightly fitted over the end213aa of the first worm gear 213a. The endless belt 214c is trainedaround the drive and driven pulleys 214a, 214b.

With respect to a plane P formed by the first power transmission means,i.e. the plane of the base plate 216, the motor 212 is attached, on thebase plate 216, on the side opposite to the side where the reductiongear unit 213 is mounted. In other words, the motor 212 is remote fromthe lens barrel 210 while the reduction gear unit 213 is near the lensbarrel 210. Further, the motor 212 and the reduction gear unit 213 arearranged on an imaginary circumference C whose center agrees with thecenter O of the optical axis of the lens barrel 210. Specifically, themotor 212 and the velocity reduction unit 213 are arranged in the shapeof L along the outer circumference of the lens barrel 210 when viewingthe lens barrel in the direction of the optical axis (perpendicular tothe plane shown in FIG. 18).

The base plate 216 has a protector 216f for enclosing and protecting theendless belt 214c, as shown in FIGS. 18 and 19. The base plate 216 alsohas a coupling member 216h via which the drive system is coupled to abody of the device such as a video tape recorder as shown in FIGS. 19and 20.

In operation, when the motor 212 is rotated forwardly or backwardly,rotational force of the motor 212 is transmitted via the first powertransmission means 214 to the first worm gear 213a, which receives therotational force having a reduced velocity. The rotational force of thefirst worm gear 213a rotates the first worm wheel 213b at a much reducedvelocity. The rotational force of the first worm wheel 213b istransmitted to the second worm wheel 213d at a further reduced velocityvia the second worm gear 213c integral with the first worm wheel 213b.The second worm wheel 213d rotates the output shaft 215. The rotationalforce of the output shaft 215 is transmitted via the pinion 215c tooperate the lens barrel 210.

In the foregoing embodiment, two sets of the first worm gear 213a andthe first worm wheel 213c, and the second worm gear 213c and second wormwheel 213d are employed to obtain large velocity reductions of the motor212 and assure very quiet operation.

It should be noted that this invention is not limited to the double-wormconfiguration but is applicable to other configurations. Although thefirst worm gear 213a in parallel with the drive shaft 212a of the motor212 and the first worm wheel 213b are indispensable, the componentssucceeding the second worm gear may be reduction gear trains includingspur gears.

As shown in FIG. 22, a reduction gear train 214A may be used as thefirst power transmission means for transmitting the rotational force ofthe motor 212 to the velocity reduction unit 213 (FIG. 21). The geartrain 214A includes a small drive gear 214Aa tightly fitted over thedrive shaft 212a, and a large driven gear 214Ab tightly fitted over theshaft 213aa of the first worm gear 213a. An idle gear may be insertedbetween the gears 214Aa and 214Ab. In FIG. 22, the componentscorresponding to or similar to those shown in FIG. 18 are denoted by thecorresponding or similar reference numerals, and will not be describedin detail.

With the foregoing embodiment, the velocity-reduced drive system iscompact, being able to suppress noises extensively. The flat motor andthe velocity reduction unit are arranged along the cylindrical movablemember to decrease a useless space around the device to which the drivesystem is applied, which is contributive to size reduction of suchdevice.

APPLICABLE FIELDS

The velocity-reduced drive system of the invention is suitable tooperate a movable member of a video camera or a combined-camera-and-VTRunit.

What is claimed is:
 1. A velocity-reduced drive system comprising:(a) amotor housed in at least one case of a plurality of cases; and (b) areduction gear unit including a worm gear rotatably supported by atleast two of said cases, first power transmission means for transmittingrotational force of said motor to said worm gear, and second powertransmission means for transmitting the rotational force of said wormgear to an output shaft, said second power transmission means includinga worm wheel meshed with said worm gear.
 2. A velocity-reduced drivesystem according to claim 1, wherein said first power transmission meansincludes pulleys fitted over a drive shaft of said motor and a shaft ofsaid worm gear, respectively, and an endless belt trained over saidpulleys, and said second power transmission means includes a gear train.3. A velocity-reduced drive system according to claim 1, wherein saidfirst power transmission means includes pulleys respectively fitted overa drive shaft of said motor and a first worm shaft of said worm gear,and an endless belt trained around said pulleys, and said second powertransmission means includes a second worm shaft having an integratedworm wheel meshed with said worm gear, and a second worm wheel integralwith said output shaft and engaged with a worm gear of said second wormshaft.
 4. The velocity-reduced drive system of claim 1, wherein one ofsaid plurality of cases is a housing for said motor.
 5. Thevelocity-reduced drive system of claim 4, wherein said one of saidplurality of cases which houses said motor is connected to another ofsaid plurality of cases, and further wherein a remainder of saidplurality of cases other than said one house said reduction gear unit.6. The velocity-reduced drive system of claim 4, wherein said pluralityof cases includes first and second cases which rotatably support saidworm gear, and wherein said first power transmission means is disposedin said first case.
 7. The velocity-reduced drive system of claim 6,wherein said first and second cases are fastened together.
 8. Thevelocity-reduced drive system of claim 6, wherein said output shaft issupported by said first and second cases.